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Dihedral angle
About: Dihedral angle is a research topic. Over the lifetime, 15718 publications have been published within this topic receiving 174904 citations.
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TL;DR: In this paper, the effect of substitution by additional CC bonds in α-, β- and γ-positions of the 13C-αC-βC-γH bond fragment is elucidated.
Abstract: 13C, 2H spin–spin coupling constants over one, two and three bonds were measured from the 100-MHz 13C NMR spectra of deuteriated isotopomers of norbornane-d1, (1) and fenchane-2-d1 (2) and also of a number of mono-deuteriated alkyl-substituted adamantanes. The magnitudes of the corresponding J(13C, 1H) values derived from these data by application of the well known relationship J(X, 1H) = 6.5144J(X, 2H) are discussed with respect to the structural data for the hydrocarbons, which were taken from force field calculations with the Allinger MM2 method. In particular, the dihedral angle dependence and the Karplus curve for 3J(13C, 1H) are investigated. Coupling constants calculated by the FP-INDO method are compared with the experimental data, and the effect of substitution by additional CC bonds in α-, β- and γ-positions of the 13C-αC-βC-γH bond fragment is elucidated. If substituent effects that arise through branching and methyl substitution in 1 and 2 are taken into account for dihedral angles ϕ > 90°, one derives 3J(13C, 1H) = 4.50 − 0.87 cos ϕ + 4.03 cos 2ϕ with J(0°) = 7.7, J(60°;) = 2.0 and J(180°) = 9.4 Hz.
82 citations
TL;DR: The experimental data are found to be in excellent accord with an oriented dipole model, rather than with the averaged dipoles model conventionally assumed for FRET.
Abstract: The efficiency of fluorescence resonance energy transfer (FRET) between two chromophores positioned at opposite ends of DNA base pair domains has been investigated. The base pair domain serves as a helical scaffold which defines both the distance between chromophores and the dihedral angle between their electronic transition dipole moments, each incremental base pair increasing the distance and stepping the dihedral angle. Fluorescence quantum yields and lifetimes have been determined for both the donor and acceptor chromophores. The experimental data are found to be in excellent accord with an oriented dipole model, rather than with the averaged dipole model conventionally assumed for FRET.
82 citations
82 citations
TL;DR: It is shown that the distribution of ϕ/ψ angles for all 87,000 residues in these proteins shows the same dependence on τ as predicted by Ramachandran and colleagues, making clear that steric constraints alone are sufficient to explain the backbone dihedral angle distributions observed in proteins.
Abstract: The pioneering work of Ramachandran and colleagues emphasized the dominance of steric constraints in specifying the structure of polypeptides. The ubiquitous Ramachandran plot of backbone dihedral angles (f and c) defined the allowed regions of conformational space. These predictions were subsequently confirmed in proteins of known structure. Ramachandran and colleagues also investigated the influence of the backbone angle s on the distribution of allowed f/c combinations. The ''bridge region'' (f � 0 and 220 � c � 40) was predicted to be particularly sensitive to the value of s. Here we present an analysis of the distribution of f/c angles in 850 non- homologous proteins whose structures are known to a resolution of 1.7 Aor less and sidechain B- factor less than 30 A ˚ 2 . We show that the distribution of f/c angles for all 87,000 residues in these proteins shows the same dependence on s as predicted by Ramachandran and colleagues. Our results are important because they make clear that steric constraints alone are sufficient to explain the backbone dihedral angle distributions observed in proteins. Contrary to recent suggestions, no additional energetic contributions, such as hydrogen bonding, need be invoked.
82 citations
TL;DR: In this article, 1-[N-(4-chlorophenyl)]aminomethylidene-2(1H)naphthalenone (C17H12NOCl) (1) was synthesized and the crystal structure was determined.
Abstract: 1-[N-(4-chlorophenyl)]aminomethylidene-2(1H)naphthalenone (C17H12NOCl) (1) was synthesized and the crystal structure was determined. Compound 1 crystallizes in the monoclinic space group P21/n with a = 4.761(3) A, b = 20.347(1) A, c = 13.773(2) A, β = 92.89(3)°, V = 1332.4(3) A3, Z = 4, D
c = 1.404 g cm−3, μ(Mo Kα) = 0.28 mm−1, and R = 0.036 for 2680 reflections [I > 2σ(I)]. Molecule 1 is not planar, and the dihedral angle between the naphthaldeyde plane A [C1–C11, 01] and the 4-chloroaniline plane B [C12–C17, C11, N1] is 20.1(3)°. An intramolecular hydrogen bond occurs between the hydroxyl oxygen and imine nitrogen atoms [2.528(3) A]. IR, 1H NMR, and UV measurements and AM1 semiempirical quantum mechanical calculations support the keto form found in the X-ray structure.
82 citations